Updated URLs in docs

Looking at the help files, I noticed the URLs for the rrd documentation has been changed.

from www/html/howtograph.html http://people.ee.ethz.ch/~oetiker/webtools/rrdtool/doc/rrdcreate.en.html is now http://oss.oetiker.ch/rrdtool/doc/rrdcreate.en.html

http://people.ee.ethz.ch/~oetiker/webtools/rrdtool/doc/rrdgraph.en.html is now http://oss.oetiker.ch/rrdtool/doc/rrdgraph.en.html

And

from www/html/install.html http://people.ee.ethz.ch/~oetiker/webtools/rrdtool/ is now http://oss.oetiker.ch/rrdtool/

-- Matthew Davis http://familycampground.org/matthew/